tailieunhanh - English for students of Physics_Unit 12

Scientists still do not know exactly what causes the earth’s magnetic field. In the 16th century, it was believed that a mountain of magnetite (a magnetic mineral) was located at the North Pole and that this mountain caused the earth’s magnetic field. English physician William Gilbert was the first to propose, in 1600, that the earth itself was a massive magnet. Current theories hold that the earth’s magnetic field is created by currents within the liquid outer core of the earth, which is composed mostly of iron. This liquid core contains ions, or electrically charged atoms and molecules. The. | 106 Unit Twelve MAGNETISM READING PASSAGE Earth s magnetic field Scientists still do not know exactly what causes the earth s magnetic field. In the 16th century it was believed that a mountain of magnetite a magnetic mineral was located at the North Pole and that this mountain caused the earth s magnetic field. English physician William Gilbert was the first to propose in 1600 that the earth itself was a massive magnet. Current theories hold that the earth s magnetic field is created by currents within the liquid outer core of the earth which is composed mostly of iron. This liquid core contains ions or electrically charged atoms and molecules. The motion of these charged particles within the earth is thought to create the earth s magnetic field. Scientists sometimes find it easier to model the earth s magnetic field as if it were a perfectly symmetrical magnetic field coming from one large bar magnet. The poles of this hypothetical magnetic field based on averaging the direction and strength of earth s magnetic field are called the geomagnetic poles. The north geomagnetic pole is located near Thule Greenland 1250 km 780 miles from the geographical North Pole. The south geomagnetic pole is located near Vostok Antarctica 1250 km 780 miles from the geographic South Pole. Paleomagnetism is the study of the earth s magnetic field in ancient times. Scientists can study the earth s ancient magnetic fields by measuring the magnetic orientation of certain rocks. When molten rock crystallizes crystals of magnetic minerals align with the earth s magnetic field. The rock thus records the direction of the earth s magnetic field at the time of its crystallization. By measuring the magnetic orientation and determining the age of such rocks scientists can measure the orientation of the earth s magnetic field at different times in the earth s history. Geologists can use systematic paleomagnetic measurements on rocks of different ages to map out the apparent movement of the earth

TỪ KHÓA LIÊN QUAN
crossorigin="anonymous">
Đã phát hiện trình chặn quảng cáo AdBlock
Trang web này phụ thuộc vào doanh thu từ số lần hiển thị quảng cáo để tồn tại. Vui lòng tắt trình chặn quảng cáo của bạn hoặc tạm dừng tính năng chặn quảng cáo cho trang web này.